Lead the returned point in sub_6FDAB940, not the path target

[ResurrectedTrader]

sub_6FDAB940 returns where a path's target unit stands, led along the target's facing by the path's dwSpeed. MOO applies the lead through PATHUtil_AdvanceTowardsTarget_6FDAB890, which adds it to the path's own tTargetCoord and returns the unled point. As a result:

• the per-step "target moved more than 5 subtiles" test (sub_6FD5DB70) compares against an unled point, and
• every call moves the path's target a bit further along the facing.

1.10f

The whole of D2Common.0x6FDAB940. esi is the output point (ecx on entry), and the lead is added there:

6FDAB940  push    ecx
6FDAB941  push    esi
6FDAB942  push    edi
6FDAB943  mov     edi, edx                          ; ptPath
6FDAB945  mov     esi, ecx                          ; pOutPathPoint
6FDAB947  test    edi, edi
6FDAB949  jnz     short loc_6FDAB969
6FDAB94B  push    201h
6FDAB950  push    6FDE55ACh
6FDAB955  push    6FDE541Ch
6FDAB95A  call    6FDC4352h
6FDAB95F  add     esp, 0Ch
6FDAB962  push    0FFFFFFFFh
6FDAB964  call    6FDC446Fh
6FDAB969  mov     ecx, [edi+58h]                    ; pTargetUnit
6FDAB96C  test    ecx, ecx
6FDAB96E  jnz     short loc_6FDAB98E
6FDAB970  push    202h
6FDAB975  push    6FDE55ACh
6FDAB97A  push    6FDE529Ch
6FDAB97F  call    6FDC4352h
6FDAB984  add     esp, 0Ch
6FDAB987  push    0FFFFFFFFh
6FDAB989  call    6FDC446Fh
6FDAB98E  mov     eax, [ecx]
6FDAB990  cmp     eax, 2
6FDAB993  jz      short loc_6FDAB9B2
6FDAB995  cmp     eax, 3
6FDAB998  jle     short loc_6FDAB99F
6FDAB99A  cmp     eax, 5
6FDAB99D  jle     short loc_6FDAB9B2
6FDAB99F  mov     ecx, [ecx+2Ch]
6FDAB9A2  test    ecx, ecx
6FDAB9A4  jz      short loc_6FDAB9AE
6FDAB9A6  push    ecx
6FDAB9A7  call    D2Common_10162
6FDAB9AC  jmp     short loc_6FDAB9B8
6FDAB9AE  xor     eax, eax
6FDAB9B0  jmp     short loc_6FDAB9B8
6FDAB9B2  mov     eax, [ecx+2Ch]
6FDAB9B5  mov     eax, [eax+0Ch]
6FDAB9B8  mov     [esi], ax                         ; out.X = target X
6FDAB9BB  mov     ecx, [edi+58h]
6FDAB9BE  mov     eax, [ecx]
6FDAB9C0  cmp     eax, 2
6FDAB9C3  jz      short loc_6FDAB9E2
6FDAB9C5  cmp     eax, 3
6FDAB9C8  jle     short loc_6FDAB9CF
6FDAB9CA  cmp     eax, 5
6FDAB9CD  jle     short loc_6FDAB9E2
6FDAB9CF  mov     ecx, [ecx+2Ch]
6FDAB9D2  test    ecx, ecx
6FDAB9D4  jz      short loc_6FDAB9DE
6FDAB9D6  push    ecx
6FDAB9D7  call    D2Common_10163
6FDAB9DC  jmp     short loc_6FDAB9E8
6FDAB9DE  xor     eax, eax
6FDAB9E0  jmp     short loc_6FDAB9E8
6FDAB9E2  mov     ecx, [ecx+2Ch]
6FDAB9E5  mov     eax, [ecx+10h]
6FDAB9E8  mov     [esi+2], ax                       ; out.Y = target Y
6FDAB9EC  mov     al, [edi+68h]                     ; dwSpeed
6FDAB9EF  test    al, al
6FDAB9F1  jz      short loc_6FDABA49
6FDAB9F3  mov     edx, [edi+58h]
6FDAB9F6  mov     eax, [edx+2Ch]                    ; target's pDynamicPath
6FDAB9F9  push    eax
6FDAB9FA  call    D2Common_10158                    ; PATH_GetDirection
6FDAB9FF  xor     ecx, ecx
6FDABA01  and     eax, 0FFh
6FDABA06  mov     cl, [edi+68h]
6FDABA09  mov     [esp+0Ch+var_4], ecx
6FDABA0D  fild    [esp+0Ch+var_4]
6FDABA11  shl     eax, 3
6FDABA14  shl     ecx, 8
6FDABA17  fstp    [esp+0Ch+var_4]
6FDABA1B  sub     eax, ecx
6FDABA1D  and     eax, 1FFh                         ; (8 * dir - (speed << 8)) & 0x1FF
6FDABA22  mov     edi, eax
6FDABA24  push    edi
6FDABA25  call    6FDC440Ch                         ; cos LUT
6FDABA2A  fmul    [esp+0Ch+var_4]
6FDABA2E  call    6FDC4FD0h                         ; _ftol
6FDABA33  add     [esi], ax                         ; <== out.X += lead
6FDABA36  push    edi
6FDABA37  call    6FDC4406h                         ; sin LUT
6FDABA3C  fmul    [esp+0Ch+var_4]
6FDABA40  call    6FDC4FD0h
6FDABA45  add     [esi+2], ax                       ; <== out.Y += lead
6FDABA49  pop     edi
6FDABA4A  pop     esi
6FDABA4B  pop     ecx
6FDABA4C  retn

PATHUtil_AdvanceTowardsTarget_6FDAB890 is the other variant. It has the same lead but adds it to the path's target (esi = ptPath there):

6FDAB8DB  mov     eax, [eax+2Ch]
6FDAB8DE  push    edi
6FDAB8DF  push    eax
6FDAB8E0  call    D2Common_10158                    ; PATH_GetDirection
6FDAB8E5  xor     ecx, ecx
6FDAB8E7  and     eax, 0FFh
6FDAB8EC  mov     cl, [esi+68h]
6FDAB8EF  mov     [esp+0Ch+var_4], ecx
6FDAB8F3  fild    [esp+0Ch+var_4]
6FDAB8F7  shl     eax, 3
6FDAB8FA  shl     ecx, 8
6FDAB8FD  fstp    [esp+0Ch+var_4]
6FDAB901  sub     eax, ecx
6FDAB903  and     eax, 1FFh
6FDAB908  mov     edi, eax
6FDAB90A  push    edi
6FDAB90B  call    6FDC440Ch
6FDAB910  fmul    [esp+0Ch+var_4]
6FDAB914  call    6FDC4FD0h
6FDAB919  add     [esi+10h], ax                     ; ptPath->tTargetCoord.X += lead
6FDAB91D  push    edi
6FDAB91E  call    6FDC4406h
6FDAB923  fmul    [esp+0Ch+var_4]
6FDAB927  call    6FDC4FD0h
6FDAB92C  add     [esi+12h], ax                     ; ptPath->tTargetCoord.Y += lead
6FDAB930  pop     edi
6FDAB931  pop     esi
6FDAB932  pop     ecx
6FDAB933  retn

1.14d

The same in DRLGPATH_GetMissileTargetPosition (Game.exe 0x679250):

00679250  push    ebp
00679251  mov     ebp, esp
00679253  sub     esp, 0Ch
00679256  push    esi
00679257  push    edi
00679258  mov     edi, edx                          ; ptPath
0067925A  test    edi, edi
0067925C  mov     esi, ecx                          ; pOutPathPoint
0067925E  jnz     short loc_67927F
00679260  push    201h
00679265  call    GetAddress
0067926A  push    eax
0067926B  push    offset Default
00679270  call    ERROR_UnrecoverableInternalError_Halt
00679275  add     esp, 0Ch
00679278  push    0FFFFFFFFh
0067927A  call    _exit
0067927F  mov     ecx, [edi+58h]
00679282  test    ecx, ecx
00679284  jnz     short loc_67928D
00679286  push    202h
0067928B  jmp     short loc_679265
0067928D  mov     eax, [ecx]
0067928F  cmp     eax, 2
00679292  jz      short loc_6792B1
00679294  cmp     eax, 3
00679297  jle     short loc_67929E
00679299  cmp     eax, 5
0067929C  jle     short loc_6792B1
0067929E  mov     ecx, [ecx+2Ch]
006792A1  test    ecx, ecx
006792A3  jz      short loc_6792AD
006792A5  push    ecx
006792A6  call    GetXPos
006792AB  jmp     short loc_6792B7
006792AD  xor     eax, eax
006792AF  jmp     short loc_6792B7
006792B1  mov     eax, [ecx+2Ch]
006792B4  mov     eax, [eax+0Ch]
006792B7  mov     [esi], ax                         ; out.X = target X
006792BA  mov     ecx, [edi+58h]
006792BD  mov     eax, [ecx]
006792BF  cmp     eax, 2
006792C2  jz      short loc_6792E1
006792C4  cmp     eax, 3
006792C7  jle     short loc_6792CE
006792C9  cmp     eax, 5
006792CC  jle     short loc_6792E1
006792CE  mov     ecx, [ecx+2Ch]
006792D1  test    ecx, ecx
006792D3  jz      short loc_6792DD
006792D5  push    ecx
006792D6  call    GetYPos
006792DB  jmp     short loc_6792E7
006792DD  xor     eax, eax
006792DF  jmp     short loc_6792E7
006792E1  mov     ecx, [ecx+2Ch]
006792E4  mov     eax, [ecx+10h]
006792E7  mov     [esi+2], ax                       ; out.Y = target Y
006792EB  cmp     byte ptr [edi+68h], 0             ; dwSpeed
006792EF  jz      short loc_679370
006792F1  mov     edx, [edi+58h]
006792F4  mov     eax, [edx+2Ch]
006792F7  push    eax
006792F8  call    GetDirection_0                    ; PATH_GetDirection
006792FD  movzx   ecx, byte ptr [edi+68h]
00679301  movzx   eax, al
00679304  add     eax, eax
00679306  add     eax, eax
00679308  mov     [ebp+var_8], ecx
0067930B  add     eax, eax
0067930D  shl     ecx, 8
00679310  fild    [ebp+var_8]
00679313  sub     eax, ecx
00679315  and     eax, 1FFh                         ; (8 * dir - (speed << 8)) & 0x1FF
0067931A  mov     edi, eax
0067931C  push    edi
0067931D  fstp    [ebp+var_8]
00679320  call    MATH_sinTable_f32_LookupOffset
00679325  push    edi
00679326  fmul    [ebp+var_8]
00679329  fnstcw  [ebp+var_2]
0067932C  movzx   eax, [ebp+var_2]
00679330  or      eax, 0C00h
00679335  mov     [ebp+var_C], eax
00679338  fldcw   word ptr [ebp+var_C]
0067933B  fistp   [ebp+var_C]
0067933E  mov     cx, word ptr [ebp+var_C]
00679342  add     [esi], cx                         ; <== out.X += lead
00679345  fldcw   [ebp+var_2]
00679348  call    MATH_sinTable_f32_Lookup
0067934D  fmul    [ebp+var_8]
00679350  fnstcw  [ebp+var_2]
00679353  movzx   eax, [ebp+var_2]
00679357  or      eax, 0C00h
0067935C  mov     [ebp+var_C], eax
0067935F  fldcw   word ptr [ebp+var_C]
00679362  fistp   [ebp+var_C]
00679365  mov     dx, word ptr [ebp+var_C]
00679369  add     [esi+2], dx                       ; <== out.Y += lead
0067936D  fldcw   [ebp+var_2]
00679370  pop     edi
00679371  pop     esi
00679372  mov     esp, ebp
00679374  pop     ebp
00679375  retn

Change

Apply the lead to pOutPathPoint in sub_6FDAB940. PATHUtil_AdvanceTowardsTarget_6FDAB890 still serves its other caller, PATH_UpdateTargetUnit (at solve time), which does move the path target; that call is unchanged. Not version-gated, since 1.10f and 1.14d agree.

🤖 Generated with Claude Code